Magnetohydrodynamic generator



FIPEQE ULMMUM MUUM Nov. 28, 1967 R. GEBEL 3,355,608

MAGNETOHYDRODYNAMI C GENERATOR Filed July 3l, 1964 3 Sheets-Sheet l FIG.1

Nov. 28, 1967 Y R. GEBEL 3,355,608

MAGNETOHYDHODYNAMIC GENERATOR Filed July 5l, 1964 3 Sheets-Sheet 2 FIG.3

Nov. 2s, 1967 l R. GEBEL 3,355,608

MAGNETOHYDRODYNAMIC GENERATOR Y Filed July 31, 1964 s sheets-Sheet :s

R s T mi mi n mnd fum mrd L'lfa' 1 b .LJL' .b JL Ib FIG. 5

United States Patent O 3,355,608 MAGNETOHYDRDYNAMIC GENERATOR RudolfGebel, Erlangen, Germany, assignor to Siemens- SchuckertwerkeAktiengesellschaft, Berlin-Siemensstadt, Germany, a corporation ofGermany Filed July 31, 1964, Ser. No. 386,652 Claims priority,application Germany, Aug. 2, 1963,

6 claims. (cl. 31o- 11) My invention relates to magnetohydrodynamicgenerators, also called magnetoplasmadynamic generators and hereinafterbrieiiy called MHD-generators.

In such generators, electrical energy is derived from a rapid flow of aworking medium consisting of an ionized gas or plasma. When the plasmaor its rapid iiow is produced thermally, the generator directly convertsthermal energy into electrical energy. So-called seed materials areadded to the plasma for increasing the degree of ionization and theconductivity of the working gas. In order to produce electrical energy,the plasma is passed through a magnetic eld transverse to the flow paththereof. A utilizable electromotive force is then generated betweenelectrodes spaced from each other in a direction perpendicular to thedirection of plasma flow and perpendicular to the magnetic field. Aparticularly compact construction is obtainable when the plasma isguided in a helical path. Therefore, it has been suggested that theplasma be passed between coaxial electrodes in an axial unidirectionalmagnetic field in a helical path. As a result, the generated electriccurrent is a direct current.

For directly producing an alternating current of electricity, one of thecontrolling quantities or factors of current generation must be variedperiodically. Thus, for example, traveling magnetic fields and rotatingfields or a pulsating flow of plasma may be employed. To prevent lossesdue to short-circuiting currents in the MHD-generator, it is not onlynecessary to insulate the electrodes but also to provide means foravoiding a short-circuit through the plasma external to the appliedmagnetic field. In a known MHD-generator for producing alternatingcurrent, an axial flow of plasma between coaxial walls in a radialmagnetic field is employed for preventing losses by short-circuitcurrents. This lresults in circulating currents within the plasma whichaxially travels along with the plasma ow and which induce anelectromotive force (EMF) in a winding located downstream of the plasmachannel. The known equipment therefore requires a Winding for producingthe magnetic field and another winding for conducting away the generatedelectrical energy. The resulting rather great length of the plasmachannel having only certain regions that can be utilized for thegeneration of electric current, is a considerable disadvantage of suchequipment.

It is an object -of the invention to provide an MHD- generator which iscapable of producing alternating current with only one winding and whichalso combines a compact design and a large active portion of the channellength with an effective prevention of losses by short-circuitingcurrents. Another yobject of the invention is to provide anMHD-alternating-current generator suitable for use in power distributionnetwork systems, together with other generators, such as electrodynamicalternators, for example.

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According to the invention, an MHD-generator is provided with coaxialelectrodes between which an ionized working medium, for example a gas,is guided on a helical path within an electrically produced axialmagnetic field. In such an MHD-generator it is an essential feature ofthe invention that the electrodes are conductively connected with eachother and that the magnet winding is energized by alternating current,being preferably connected to an alternating-current supply line. Themagnet winding takes inductive reactive power out of the supply linesuch as a conventional power distribution system for producing themagnetic field in the MHDagenerator, and the same winding simultaneouslyfeeds active power into the supply line. Such a generator, therefore, isparticularly suitable for synchronous operation in power distributionsystems.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention has been illustrated and described as embodied ina magnetohydrodynamic generator, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, in which:

FIG. l shows schematically and in longitudinal section an individualMHD-generator comprising the plasma channel and the magnetic fieldwinding, the vectors of various physical quantity being indicated byarrows.

FIG. 2 Shows schematically a cross section of the generator, also withindicated vectors, along the line II-II of FIG. l.

FIG. 3 shows another embodiment of an MHDgen erator according to theinvention in longitudinal section.

FIG. 4 illust-rates schematically an MHD-generator according to theinvention connected with the distribution network otherwise energizedfrom conventional alternators in a power station.

FIG. 5 shows schematically a circuit diagram of three MHD-generatorsaccording to the invention connected to respective phases of athree-phase distribution system; and

FIG. 6 shows in longitudinal section a modification of an MHD-generatoraccording to the invention.

The same reference characters are employed in all illustrations forcorresponding components respectively.

Following is a tabulation of definitions relating to the physicalquantities entered on the drawings.

E=e1ectrica1 eld intensity between the electrodes due to the fieldintensity induced in the plasma, the electrical field intensity E beingopposed to the induced field intensity.

EH=Hall field intensity developing due to the coaction of the current Iflowing between the electrodes with the magnetic field H.

H :applied magnetic eld resulting from the exciting current Ie takenfrom the power supply line.

l=the current flowing through the electrodes and resulting from thefield intensity induced in the plasma.

IH=Hall current which flows on account of the Hall field intensity EH.

Ie=exciting current for providing the applied magnetic field H, thiscurrent being taken from the power supply line.

v=tangential component of the plasma flow.

In FIG. 1 there is shown a generator plasma channel 1 which is formedbetween electrically conducting coaxial cylinders 2 and 3 joined bylateral circular end walls 4 also electrically conducting. The walls 2,3 and 4, may consist of water-cooled high-temperature steel such as thebrand of steel available in the trade under the name Thermax steel. Thecylindrical walls 2 and 3 constitute the electrodes of the MHD-generatorand are conductively connected with each other through the end walls 4.The plasma flows into the generator channel 1 through an inlet duct 5 inthe direction indicated by an arrow and then passes on a helical paththrough the channel 1 and leaves it through an outlet 6 in the directionindicated by an arrow. The channel 1 is bounded by a ring-shaped magnetcoil 7 which produces an axial magnetic field and also serves to derivethe induced voltage and effective power from the plasma flow. Themagnetic lines of force are guided through a yoke piece 9 consisting ofa laminated stack of transformer sheet material and thus pass in axialdirections through the generator channel 1. The cylindrical shape of thechannel 1 is especially apparent from the cross section shown in FIG. 2.

When the magnet coil 7 is energized by alternating current from a powersupply line, for example at 60 c.p.s., and plasma is being passedthrough the channel 1 in the above-described manner, the MHD-generatoroperates as follows:

The tangential plasma flow v (FIGS. 1 and 2), in coaction with the axialmagnetic field H produces a radial electrical field E between theelectrodes 2 and 3. This field E is immediately balanced or equalizedthrough the conducting walls 4. The equalization results in the fiow ofa current I between the two coaxial electrodes, the current passingthrough the walls 4. Due to the radial current I a strong Hall effectresults from the axial magnetic field H which causes a circular Hallcurrent IH to fiow in the plasma between the conductively interconnectedelectrode. Since this Hall current, occurring along the entire channelaxis, has a sinusoidal Wave shape when the magnet winding 7 is traversedby sinusoidal alternating current from the power supply line, a voltageis induced in the magnet winding 7 which leads the exciting current Ieby about 90 electrical degrees and thus is proportional to theexcitation voltage and thereby aids this voltage. Consequently, inanalogy to the performance of the conventional electrodynamicgenerators, a reactive power is taken from the supply line for buildingup the magnetic field. Simultaneously, however, the magnet winding 7feeds effective power to the supply line that is available to the loadsto be energized therefrom.

It should be clear that the generator according to the inventioneliminates the need for an additional winding or coil and that it alsoentirely avoids the problem of insulation with respect to theelectrodes. The plasma channel can simply be made of conducting materialsuch as the aforementioned high-temperature steel which can be cooledwith water. Furthermore, the firing chamber used for generating oraccelerating the plasma can be connected with the generator channelwithout any insulation. In other words, the generator does not requirethe use of insulating material which, as is known, for MHD- generatorsmust be resistant to extremely high temperatures. This is importantbecause, aside from other technological difficulties, the knowninsulating materials are not as resistant as are the available specialsteels. Furthermore, losses due to conductance of electricity away fromthe electrodes through the gas outside of the magnetic field are notpossible in a generator according to the invention.

The MHD-generator shown -in FIG. 3 operates on the same principle as theone described above with reference to FIGS. 1 and 2. According to FIG.3, the magnet winding 7 is mounted within the smaller coaxial electrode3. This results in a larger channel diameter without increasing theoverall size of the entire unit. This is tantamount to increasing theutilizable flow path through the channel with a smaller winding 7. Thelarger channel diameter corresponds to lower losses at the walls for agiven plasma flow speed. For guiding the magnetic field lines, thisgenerator is provided with a core 8 and a yoke portion 9 which may bothconsist of laminated transformer sheet material.

As mentioned above, an MHD-generator according to the invention can beconnected to a power distribution system for cooperation with othergenerators of the system. This is exemplified in FIG. 4 showingschematically an MHD-generator b according to the invention connected toa power line B energized from a conventional power station A forsupplying current to a load C. The MHD- generator, as explained, iscapable of synchronous operation, deriving reactive power from thedistribution system for producing the magnetic field and furnishingactive power into the line for consumption by the load.

By providing three generators according to the invention, the generationof three-phase alternating current is afforded in an analogous manner.Thus, FIG. 5 shows schematically three MHD-generators b according to theinvention connected through respective transformers d to the phases R,S, T of the three-phase distribution system, the three transformershaving the common bus connected to a Y-point denoted by O of the system.

By substituting insulating walls for the conducting end walls 4 of theplasma channel in an MHD-generator according to the invention, thegenerators can readily be adapted for the generation of direct current.For this purpose, the magnet winding 7 is energized by direct current,and the then mutually insulated electrodes 2 and 3 then provide a directoutput voltage. A modified generator of this type is schematicallyillustrated in FIG. 6. The end walls 4 in the MHD-generator of FIG. 6,otherwise corresponding to FIG. 3, consist of insulating material. Themagnet winding 7 has its leads e connected to a directcurrent source,and the output leads f, connected to the respective cylindricalelectrodes 2 and 3, furnish the generated direct current.

-I claim:

1. A magnetohydrodynamic generator, comprising a flow channel for thepassage of ionized gaseous medium on a helical path, a magnet windingmounted -in coaxial relation to said channel for producing therein amagnetic field in the axial direction of the ow path, electrodes spacedfrom each other transversely of said path along said channel and beingconductively connected with each other, and an alternating-currentsupply line connected to said winding.

2. A magnetohydrodynamic generator, comprising two cylindricalelectrodes coaxially mounted and radially spaced from each other, saidelectrodes forming between each other a tubular channel for the fiow ofplasma on a helical path, said electrodes being conductively connectedwith each other, a magnet winding mounted in coaxial relation to saidchannel for producing therein a magnetic field in the axial direction ofthe flow path, and an alternating-current supply line connected to saidwinding.

3. A magnetohydrodynamic generator, comprising two cylindrical andaxially elongated electrodes coaxially mounted and form-ing between eachother a tubular channel for the ow of plasma on a helical path, circularend walls of conducting material joining said electrodes to each otherand forming the respective axial ends of said channel, a magnet windingmounted in coaxial relation to said channel for producing therein amagnetic field in the axial direction of the ow path, and analternating-current supply line connected to said Winding.

4. In a magnetohydrodynarnic generator according to claim 2, saidwinding being coaxially mounted on the outer one of said cylindricalelectrodes.

S. In a magnetohydrodynamic generator according to claim 2, said windingbeing coaXially mounted wtihin the inner one of said cylindricalelectrodes.

6. A magnetohydrodynamic generator according to core upon which saidWinding is seated and having lateral yoke portions joined with said coreand forming therewith an enclosure around said winding with theexception of an annular gap formed between said yoke portions, said twochannel-forming electrodes being located in said annular gap.

No references cited.

MILTON O. HIRSHFIELD, Primary Examiner.

claim 5, comprising a magnet-izable structure having a 10 D. X. SLINEY,Examiner.

1. A MAGNETOHYDRODYNAMIC GENERATOR, COMPRISING A FLOW CHANNEL FOR THEPASSAGE OF IONIZED GASEOUS MEDIUM ON A HELICAL PATH, A MAGNET WINDINGMOUNTED IN COAXIAL RELATION TO SAID CHANNEL FOR PRODUCING THEREIN AMAGNETIC FIELD IN THE AXIAL DIRECTION OF THE FLOW PATH, ELECTRODESSPACED FROM EACH OTHER TRANSVERSELY OF SAID PATH ALONG